COELENTERATA 



25 



Parker has measured the rate of transmission of the nerve 

 impulse in sea-anemones at 21- centigrade. It was found to be 

 from 121-146 mm. a second. 



Kassianow, Parker and others have studied the nervous system 

 and reactions of colonial forms. There seems to be little evidence 

 of any nervous coordination in colonial polyps, each polyp in Renilla 

 for instance when stimulated by contact seems to react independ- 

 ently of the rest. Although the common flesh which supports them 

 may bring about like changes in several or all of the members of 

 the colony, the zooids are not centers from which impulses pass to 

 other parts. 



The peduncle and rachis are probably permeated by a nerve- 

 net which extends from the zooids of the colony. 



Ctenophora. The first observations on the nervous system 

 of this group were by Pschschiltz, 1829, and later by Mertens, 1833. 

 One of the first complete summaries of the general structure of the 



Fig. 7. Two-thirds of an elonj^ate ctenophor, Mayer. B. Enlarged portion of 

 sense organ of elongate ctenophore. C. Diagram of a ctenophore, 

 Mayer. D. Sense organ of ctenophore from side showing connections 

 with the eight ciliary glands. E. Same as D from above. F. Nerve 

 plexus of a ctenophore, Hertwig. G. Apical sense organ of a cteno- 

 phore after Hertwig. H. Diagram of a ctenophoi-e, Hertwig. H. and I. 

 View of apical sense organ of a ctenophore showing its relation to the 

 ciliary bands. H from the side, I from above. J. Coenoplana from 

 above showing apical sense organ, Korotneff. K. Coenoplana sense 

 organ in section with associated ganglia, Abbott. 

 I., J., from Parker and Haswell's Zoology, permission of Macmillan Co. 



